To optimally control the powering of a synchronous motor (e.g., a brushless motor or a stepper motor), the rotor position has to be known. The rotor position can be obtained using, for example, a position sensor or sensorless technologies.
Sensorless technologies are based on the measurement of electrical parameter value and/or motor parameters, which vary as a function of the rotor position. For example:
the back EMF voltage which varies as a function of the speed and the rotor position; and
the inductance phase value which is either constant or varies as a function of the rotor position and the phase current (saturation).
Conventional methods allow for the determination of the rotor position while simultaneously measuring the back EMF voltages of the motor phases not powered. Such solutions have the advantage of a good resolution and good low speed performances. However, these conventional methods are limited for high and mid speed ranges with high torque levels.